The following invention relates to water heaters which receive solar radiation to heat water or other fluids passing through the heater.
Solar water heaters are well known in the prior art. Typical prior art solar water heaters route water along a pathway which is exposed to the sun and which is configured from materials which maximize an amount of heat that is absorbed from the solar radiation, for a transfer of this heat to the water passing through the water heater. For instance, black plastic tubing can be utilized which is placed in an area where it is exposed to solar radiation. As the water passes through an interior of the black plastic tubing, the black plastic tubing heats the water with heat that the tubing absorbs from solar radiation incident on the tubing. These and other prior art solar water heaters all suffer from a variety of different drawbacks which have inhibited the acceptance of solar water heaters for most water heating applications.
For instance, typical solar water heaters are either constructed from expensive materials making them cost prohibitive to use or are manufactured from materials which cannot withstand the extreme solar radiation environment for long periods of time, such that their performance degrades and they fail prematurely. Also, they are often not insulated to keep the water therein warm for extended periods after the solar radiation ceases. Accordingly, a need exists for a solar water heater which is constructed in a manner which keeps temperature sensitive components of the water heater within design temperature ranges for the materials and which has a simple construction and yet efficiently utilizes solar radiation to heat large quantities of water or other fluids in a relatively small amount of space.
This invention provides a solar water heater which is of simple compact construction for ease of installation and use and which automatically maintains a temperature of temperature critical components within their designed temperature ranges for efficient heating of the water or other fluids without exceeding temperature limits which would cause damage to the water heater. The water heater includes a housing with a base and side walls spaced from a recess by an insulated core. An upper rim of the water heater surrounds this recess and a lens spans this recess.
The lens is configured to transmit large amounts of solar radiation therethrough at a variety of different incidence angles, while also providing insulation against conduction heat transfer out of the water heater. The lens preferably includes a non-planar top surface which reduces reflection of the solar radiation away from the lens when the sun is at low angles of incidence upon the lens. The lens also includes voids which have an at least partial vacuum therein. This vacuum condition reduces conduction heat transfer out of the solar water heater through the lens.
An air trap is located directly below the lens. A heat absorption plate is located within the recess and below the air trap. The absorption plate receives and absorbs most of the solar radiation passing through the lens and through the air trap. This absorption plate heats up and causes heating of air within the air trap.
A liquid space is located within the recess and below the absorption plate. The liquid space is filled with a heat transfer liquid. A heat exchanger is located within the liquid space and includes walled chambers which enclose water and are coupled together by junctions so that a serpentine water path is provided through the chambers of the heat exchanger. Heat from the absorption plate heats the heat transfer liquid within the liquid space and this heat transfer liquid then heats the water through the walls of the heat exchanger. Insulation within the housing and within the lens, as well as the air trap itself, keeps the water within the chambers of the heat exchanger warm for significant periods of time even after solar radiation ceases (i.e. overnight).
Additionally, a heat control valve is provided to release air from the air trap. Preferably, the heat control valve is located within the lens and includes a cover which closes a gap in the lens when the heat control valve is closed and which opens to make a path for air into and out of the air trap when the heat control valve opens. When a temperature of air within the air trap reaches a maximum temperature, corresponding with the temperature at which damage may begin to occur to materials forming the lens, absorber plate, housing or heat exchanger, the heat control valve opens allowing colder air outside the air trap to come into the air trap and for hot air inside the air trap to be released from the air trap. When air within the air trap is reduced in temperature, heat absorbed by the absorber plate tends to be directed more into the air trap and then carried out of the solar water heater altogether, such that maximum temperatures for various components within the solar water heater are not exceeded. When the temperature of air within the air trap is below this maximum threshold temperature, the heat control valve closes and the air trap is allowed to trap the air and allow the air to increase in temperature. Heat absorbed by the absorber plate is then directed more efficiently into the heat transfer fluid and through the heat exchanger to the water with increased efficiency.
Accordingly, a primary object of the present invention is to provide a solar water heater which can reliably heat water over long periods of time without requiring maintenance or replacement.
Another object of the present invention is to provide a solar water heater which efficiently heats large volumes of water or other fluids in a relatively small space. Another object of the present invention is to provide a solar water heater which includes a heat control system to keep the solar water heater from exceeding maximum temperatures which would cause damage to components making up the solar water heater.
Another object of the present invention is to provide a solar water heater which can maintain a temperature of water therein over long periods of time when no solar radiation is incident upon the solar water heater.
Another object of the present invention is to provide a solar water heater which can preheat water entering a second water heater so that the second water heater utilizes less energy in boosting a temperature of water exiting the second water heater.
Another object of the present invention is to provide a solar water heater which efficiently heats water with solar radiation even when the solar radiation impacts the solar water heater at low angles of incidence.
Another object of the present invention is to provide a solar water heater which keeps the water within pathways enclosed by materials which are considered safe for drinking water.
Other further objects of the present invention will become apparent from a careful reading of the included drawing figures, the claims and detailed description of the invention.